bad service from wonga

i had three loans with Wonga loans, everything was going well, but the problem started with my third and last loan, as far as i know i have been paying this loans with a debicheck and the debit orders were going through and was not even consulted or notified by wonga if there was any missing payment extra charges on my loan. i only found out through a company by the name of Nimble group stating that i owe them and when i question them how do i owe the because i have never done business with them, they told me that they have taken over the WONGA debt. i tried to get answers from Wonga sending emails to get clarity regarding this matter but no response till today and this is affecting my credit score. can anyone assist if you have a solution or direct me to the relevant people to consult.